Make sure you have completed the Getting Started section before diving into this section.


The ArxRobot library allows the 3DoT board to communicate over bluetooth using command and telemetry Data Packets with checksum.

Commands are, as the name suggests, instructions for the robot or app to do something. Telemetry is simply data, such as the battery voltage that is communicated.

The library contains a list of Built-In Commands and telemetry labels, listed in Configure.h, such as the MOVE command, which is command number 01.

The function of these commands are defined in the library. For example, when the MOVE command is received, motors connected to the 3DoT are driven at the given speed and direction.

Example Sketches

In the Arduino IDE, navigate to File > Examples > ArxRobot_Library to open the included example sketches.

ArxRobot_Basic contains all the code needed to control a robot using the RoboPilot app.

ArxRobot_CustomCommands implements the addCustomCommand() and replaceBuiltInCommand() methods explained below to make user commands work with the RoboPilot app.

ArxRobot_ledPWM shows a simple custom command example, using a slider to adjust the brightness of an LED

Writing Custom Commands

To get started making a custom command, write a function in your arduino sketch with the following template:

void myCommand (uint8_t cmd, uint8_t param[], uint8_t n)
// Your code here

You can change myCommand to the name of your choosing, e.g. blinkLED, but the type must always be void and parameters must follow the (uint8_t cmd, uint8_t param[], uint8_t n) format.

You can use these parameters in your function.

void myCommand(uint8_t cmd, uint8_t param[], uint8_t n)
  • cmd – The command ID of your custom command
  • param[] – Command data sent by the app
  • n – Number of bytes of command data received in param[]

For example, in the ArxRobot_ledPWM example we adjust the brightness of an LED using the slider value sent from the RoboPilot app as follows:

void ledPWM (uint8_t cmd, uint8_t param[], uint8_t n)
    // param[0] is the first byte of command data received from the app,
    // which holds the slider value
    analogWrite(LED, param[0]);

Adding Custom Commands

Next, to add the function as a custom command that the app can call, simply call the following function in the setup portion of your code:

void ArxRobot::addCustomCommand(fptr_t function, uint8_t commandID)
  • function – Name of function to add to custom commands list
  • param[] – Command ID to associate with function

For example:

void setup()

    ArxRobot.addCustomCommand(myCommand, 0);
    ArxRobot.addCustomCommand(myOtherCommand, 1);

In the setup() of this sketch, we are adding “myCommand” and “myOtherCommand” as two custom commands, with IDs 0 and 1.

If you now create a custom command in the RoboPilot app with ID 0, it will call myCommand, and a command with ID 1 will call myOtherCommand.

Built-In Commands

In its current state, the RoboPilot App only uses the Move and Ping Commands. Functionality for other commands in being ported over from the previous app.

Name ID params[]
MOVE 0x01 [0] = Left Direction, [1] = Left Speed, [2] = Right Direction, [3] = Right Speed
CAMERA_MOVE 0x02 [0-1] = Pan, [2-3] = Tilt
READ_EEPROM 0x06 [0-1] = Address, [2] = Number of Bytes to Read
WRITE_EEPROM 0x07 [0-1] = Address, [2] = Number of Bytes to Write, [3-(2+N) = Data
SLEEP 0x0A  
COMM_SETUP 0x10 [0] = Mode ID
PING 0x11  

Replacing Built-In Commands

When using, for example, the D-pad or Tank controls on the app, the built-in MOVE command is called. If you wish to make the controls call your own function instead, simply write a custom command as explained in Writing Custom Commands, then call:

void ArxRobot::replaceBuiltInCommand(uint8_t commandID, fptr_t function)
  • commandID – Command ID to associate with function. Can use macros defined above.
  • function – Name of function to add to custom commands list


void robotWalk((uint8_t cmd, uint8_t param[], uint8_t n)
   // Robot walking code here

void setup()

    ArxRobot.replaceBuiltInCommand(MOVE, robotWalk);

Data Packets

Click the “Show Console” Button in the RoboPilot app to see data packets sent and received.

A Data Packet is constructed as follows:

Packet ID, Data Length (N), Command ID, Data 0, ..., Data N, Checksum
  • Packet ID: 0xA5 for a command, 0xCA for a telemetry message
  • Data Length: The number of data bytes sent in packet
  • Command ID: The command ID. E.g. 0x01 for MOVE
  • Data[n]: Data bytes
  • Checksum: XOR all the previous byte values to obtain checksum